Motor control system for recording instruments



I Oct. 31, 1950 T. A. COHEN 2,527,797

\(OTOR CONTROL SYSTEM FOR REQORDING INSTRUMENTS Filed Nov. 3, 1945 24 fl2g ZZZ? Patented Oct. 31, 1950 MOTOR CONTROL SYSTEM FOR RECORDINGINSTRUMENTS Theodore A. Cohen, Chicago, 11]., assignor to WheeiooInstruments Company, a corporation oi Illinois Application November 3,1945, Serial No. 628,510

9 Claims. (Cl. 318-32) 1 This invention relates to recording instrumentsand more particularly to electrical instruments for recording and/orcontrolling the value oi a condition such, for example, as temperature,

7 pressure or the like.

One of the objects of the invention is to provide a recording instrumentin which the tendency to hunt is compensated electrically so that astable and sensitive response is obtained.

Another object is to provide an instrument in which the degree ofcompensation and, thereiore, the sensitivity of the instrument can beeasily adjusted.

Still another object is to provide an instrument in which the voltagegenerated by the shaded pole windings of a reversible shaded pole motormay be utilized to provided compensation to prevent hunting.

A further object is to provide an instrument employing a shaded polemotor which is so controlled as to produce a dynamic braking eiiect toprevent overrunning or coasting.

The above and other objects and advantages of the invention will be morereadily apparent from the i'ollowing description when read in connectionwith the accompanying drawing, in which the single figure is a circuitdiagram oi an instrument embodying the invention.

The instrument illustrated is adapted to record and may, if desired, beutilized to control a variable physical condition such, for example, astemperature or pressure. For this p rpose the instrument comprises asensitive unit Ill for producing movement of a pointer II in response tovariations in the condition. The unit It may be any desired type of unitsuch as a millivolt meter instrument, a thermocouple instrument or otherpressure or temperature sensitive devicm which will move the pointer toa position dependent upon the instantaneous value of the pressure,temperature or like condition to be recorded. The pointer ii carries oneelement of a variable reactance device shown as a metal iiag I! whichmoves with the pointer. The flag i2 is adapted to move between a pair oicoils It so that the reactanoe oi the coils will vary with the extent towhich the flag p jects between them. The coils are carried by an arm llwhich is adapted to be turned to follow the motion of the pointer II bya reversible motor shown as a shaded pole motor having a main winding llconnected toa source of alternating current it and a pair of shaded polewindings II and II.

The variable reactance device may form a part resistor is.

of an oscillator circuit oi the type more particularly ducribed in myPatent No. 2,228,183, issued January 7, 1941. As shown, the coils ii areconnected through the condensers Ito. and "b to the control circuit 0!vacuum tube II in a portion of an oscillator circuit. One side oi thecoils is connected to the cathode I! of the tube 2i through condenserIla and the other side is connected to the control grid 23 throughcondenser llb. The plate 2| of the tube is connected through a platetank circuit including an inductance coil 25 and a condenser 28 to asource of supply of alternating current illustrated at 21. The platecircuit is connected through a load resistor 28 and a second source ofalternating current 29 to the cathode 22. A bypass condenser ii isconnected across the plate circuit to prevent the now of high frequencyoscillatory currents through the alternating current sources Hand 29which may bewindlngs on a power transformer. 1

The steady state output of the tube II ,is amplitled by a tube 32including a cathode II, a control grid 84 and a plate 3!. ll isconnected across the load resistor It so that the tube 32 will becontrolled partially in response to the voltage drop across the resistor20. The plate 35 of tube 32 is connected to a source of alternatingcurrent 38 which may be a winding on the power transformer including thesources 27 and 29 to one end of a relay coil ll. A condenser II isconnected across the relay coil and the opposite end of the coil isconnected through a wire 39 to the resistor 28.

Feed back to the tube ii is provided by a wire ll from a tap upon coil31 at the necessary point to produce the desired feedback voltage andconnected to the grid 23 of the tube 2i through a resistor 42. It willbe seen that the oscillator and amplifier circuits as so far describedare substantially similar to those described and claimed in my PatentNo. 2,228,163. In this circuit, when the flag i2 extends partiallybetween the coils", the instrumentis in its normal or neutral positionso that the oscillator will produce a predetermined output current. Thisoutput current will produce a voltage drop across the resistor 28 whichcauses the amplifier tube 32 to supply a predetermined normal current tothe relay coil II.

Upon movement of the pointer ii to move the flag l2 away from the coilsit, the tuning of the oscillator will be varied to increase itsoscillation and to reduce the voltage drop acrqssithe This reduces thebias on the control The control grid effect of the relay coil. j witch Mis open, a voltage will be induced in the -winding I! which will beimpressed across the ass-1,701

grid 3| causing an increase in the plate current oi the tube 32 toincrease the current flow through the relay coil 31. Similarly. if theflag I! tends to move further into the coils, the plate current of thetube 32 will be reduced to decrease the current through the relay coil.As explained in my patent, referred to above, the changes in the currentthrough the relay coil will rise and fall sharply upon movement of theflag to produce a sensitive control.

The relay coil 31 is utilized to control. the shaded pole motor througha pair of switches. and 44. The switch 43 is connected across the shadedpole winding II and is normally biased to a closed position to be openedby the relay coil in response to a predetermined current iiow therein.The switch 44 is connected across the shaded pole winding l1 and isnormally biased to an open position to be closed in response to asmaller predetermined current'in the relay coil. When the normal currentis flowing through the relay coil, the switch ll will be moved to aclosed position but the current in the coil is not sumcient to open theswitch 43 so that both windings i1 and i8 are short circuited and themotor is held stationary. Upon an increase in current above the normalflow, the switch 43 will be opened by the relay coil to cause the motorto operate in one direction while a decrease in cur-- rent below thenormal flow will allow the switch 44 to open to cause the motor to turnin the opposite direction.

One of the advantages of this type of control is that it provides adynamic braking eii'ect in the motor causing prompt stoppage of themotor upon closing of both switches. With the motor operating in eitherdirection, depending upon which switch is open, it would normally tendto coast upon operating the control to interrupt its movement. With thepresent construction, however, short circuiting of the shaded polewindings produces a dynamic braking effect in the motor which will causeit to stop quickly so that it will not tend to coast beyond the desiredcontrol position.

In order to compensate for any tendency of the instrument to hunt,compensating windings l and 46 are provided, magnetically associatedwith the relay coil 31. The winding 45 is connected through a variableresistor 41 and a rectitier 48 across the shaded pole windin i8 and thewinding 45 is similarly connected through a variable resistor 49 and arectifier SI across the shaded pole winding i1. When the switch 43 isopened a voltage will be induced in the winding it which will beimpressed across the compensating winding 45 in a direction to opposethe Similarly, when the winding 46 in a direction to oppose the effectof the relay coil. The effect of the compensating windings can be variedby adjusting the resistors 41 and 49 which are preferably coupled forsimultaneous adjustment so that the sensitivity or the control range ofthe instrument can easily be adjusted.

In a typical example assume that the flag I! is further between thecoils it than its normal position so that the current flow through therelay coil 31 is less than normal and the switch II is open. At thistime the winding ll is energized to oppose the flux in the relay coil 11so that the switch M will remain open until the flag 4llhasbeenmovedoutoithecoils ilinanamount slightly greater than themaximum position of the flag between the coils for the stable controlrange. As soon as the switch 44 is closed. the compensating eflect ofwinding u is removed. and atthistime the flag I! ispositionedatsubstantiaily the center of its permissible range of movement so thatthe instrument is operating substantially at the center oi its controlrange and will not tend to hunt or flutter on minor changes which do notcarry the instrument beyond its control range. Upon a control operationin the opposite direction with the switch 4! opened, the current in therelay coil 31 will be above normal and the motor will turn in adirection to move the coils ll toward the flag II. At

- this time the voltage induced in the winding ll Iii will be impressedon the winding 4! in a direction to assist the flux of the relay coil sothat the switch 43 will be retained open slightly longer than it wouldif the winding II were not present. This operation again brings theinstrument to a condition substantially in the center of its controlrange when the switch 43 is allowed to close. Thus a very stableoperation in both directions is produced without hunting and withoutadversely affecting the sensitivity of the instrument.

To record the condition sensed by the unit ll, any desired type ofrecording and/ or control mechanism may be provided. As shown, the motoris connected to a pen 52 which move over a chart 53 driven by a motor Ito provide a continuous record of changes in the condition. It will beunderstood that this recorder is shown only for purposes of illustrationand that any desired type oi mechanism for recording or for controllingthe condition might be operated by the motor.

While one embodiment of the invention has been shown and described indetail, it will be understood that this is illustrative only and is notintended as a definition of the scope of the invention, reference beinghad for this purpose to the appended claims.

What is claimed is:

1. In a recording instrument, a reversible motor having a pair ofreversing windings, switches for controlling the windings respectively,a relay coil for operating the switches, a circuit to supply a normalcurrent to relay coil, which relay coil operates one of the switcheswhen its current is above normal and the other of the switches when itscurrent is below normal means responsive to a condition to be recordedto vary from normal the flow of current through the relay coil, meansoperated by the motor to return to normal the flow of current throughthe relay coil upon a deviation thereof from normal in response to thelast named means, a compensating winding magnetically associated withthe relay coil, and means controlled by the switches to supply a currentto the compensating winding opposing the effect of a deviation fromnormal of the current in the relay coil.

2. In a recording instrument, a reversible motor having a pair ofreversing windings, switches for controlling the windings respectively,a relay coil for operating the switches, a circuit to supply a normalcurrent to relay coil, which relay coil operates one of the switcheswhen its current is above normal and the other of the switches when itscurrent is below normal means responsive to a condition to be recordedto vary from normal the how of current through the relay coil, means 1soperated by the motor to return to normal the tlow'of current'throughthe relay coil upon a deviation thereof from normal in'response to thelast named means, and a'pair of compensating windings magneticallyassociated with the relay coil and controlled by the switchesrespectively,

the compensating windings being so arranged that they will oppose theeffect of a deviation from v normal of the current in the relay coil.

3. In a recording instrument, a reversible shaded pole motor having apair of shaded'pole windings, a pair of switches connected across thewindings respectively, a relay coil for operating the switches, meansresponsive to a condition to be recorded to control the current in therelay coil, means operated by the motor to return to normal the currentin the relay coil upon a deviation thereof from normal in response tothe last named means, and a pair of compensating windings magneticallyassociated with the relay coil and connected across the shaded polewindings respectively, the'compensating windings being so arranged thatthey will oppose the efl'ect of a deviation from normal in the relaycoil.

' 4. In a recording instrument, a reversible shaded pole motor having apair of shaded pole windings, a pair of switches connected across thewindings respectively, a relay coil for operating the switches, theswitches being so constructed anda'rranged that they will both be closedin response to normal current in the relay coil, one will open inresponse to reduced current and the other will open in response toincreased current, means responsive to a'condition to be recorded tocontrol the current-in the relay coil, means operated by the motor toreturn to normal the current in therelay coil upon a deviation thereoffrom normal in response to the last named means, and a pair ofcompensating windings magnetically associated with the relay coil andconnected across the shaded polewindings respectively, the compensatingwindings being so arranged that theywill oppose the eflect of adeviation from normal in the relay coil.

5. In ,a recording instrument, a reversible shaded pole motor having apair of shaded pole windings, a pair of switches connected across thewindings respectively, a relay coil for operating 4 the switches, meansresponsive to a condition to be recorded to control the current in therelay coil, means operated by the motor to return to normal the currentin the relay coil upon a deviation thereof from normal in'response tothe last named means, a pair of compensating windings magneticallyassociated with the relay coil and connected across the shaded polewindings respectively', and rectiflers in circuit with the compensatingwindings of'a polaritysuch that the compensating windings will opposethe eflect of a deviationfrom normal in the relay current.

6. In a recording instrument, an oscillator circuit, means for'tuningthe oscillator circuit to vary its output including a pair of relativelymovable reactance elements, means responsive to a condition to berecorded to move one of the reactanceelements, a reversible motor tomove the other reactance element to follow up said one reactance elementin such a manner as to return coil, and means controlled by the relaycoil to supply a compensating current to the compensating winding tooppose the effect of a deviation from normal of the current in the relaycoil.

7. In a recording instrument, .an oscillator circuit, means for tuningthe oscillator circuit to vary its output including a pair of relativelymovable reactance elements, means responsive to a condition to berecorded to move one of the reactance elements, a reversible motor tomove the other reactance element to follow up said one reactance elementin such a. manner as to return the output of th oscillator circuit to anormal value upon a deviation thereof from normal, a relay coilresponsive to the output of the oscillator, a pair of switches operatedby the relay coil to control operation of the motor, and a pair ofcompensating windings controlled by the switches respectively and soarranged rela tive to the relay coil as to oppose the effect of adeviation from normal of the current in the relay coil.

8. In a recording instrument, an oscillator circuit, means for tuningthe oscillator circuit to vary its output including a pair of relativelymovable reactance elements, means responsive to a condition to berecorded to move one of the reactance elements, a reversible motor tomove the other reactance element to follow up said one reactance elementin such a manner as to return the output of theoscillator circuit to anormal value upon a deviation thereof from normal, the motor being ashaded pole motor having a pair, of'shaded pole windings. a pair ofswitches to short circuit the respectively, a relay coil responsive tothe output of the, oscillator to control the switches, compensatingwindings magnetically associated 'with the relay coil and connectedacross the shaded pole windings respectively, and rectifiers. connectedto the compensatirm windings of such polarity that the compensatingwindings oppose the effect of a deviation from-"normalof the current inthe relay coil.

9. In a recording'instrument, a reversible motor, circuitcontrolfelements for controlling the motor, a coil foroperating thecircuit control elements to cause the motorto run in one direction orthe other in accordance with currentflow through the coil, a pointer,means responsive to a condition to be recorded to move'the pointer, 50 afollower movable adjacent the pointer, a connection from the motor tothe follower, cooperat ing means on the pointer and the follower-toproduce a variation in anelech'ical eflect in response to a change inthe relative position of the '55 pointer and-the follower, meansresponsive to said electrical effect tooontrol the current flow throughthe coil, a compensating winding adjacent and magnetically related tothe .coil, and means controlled by the control elements to supply acompensating current to the winding opposing the eflect of a deviationfrom normal of the current in the coil.

'rmronons A. com.

nmarmcas' crrnn The following referencm are of record in thenleofthispatenta' 1 t UNITED STATES PATENTS Number Name Date 2,126,910Moseley- Aug. 16, 1938 2,153,986 MacLaremJr. Apr. 11, 1939 2,277,658Evans Mar. 24, 1942 2,287,002 Moseley June'l6, 1942 Allwein June a;

